Control of hydrogen embrittlement



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v v CONTROL OF HYDROGEN EMBRITTLEMEN'T Filed April 24, 1964 xwvv INVENTODONALDJR N M Eu SIMO MYRoN LEVI Agent a United States Patent 3,297,416Patented Jan. 10, 1967 3,297,416 CONTROL OF HYDROGEN EMBRITTLEMENT IDonald; J41 Ransom, Sylmar, and Eli Simon and Myron Levine, Los Angeles,Calif., assignors to Lockheed AircraftiiCorporation, Burbank, Calif.

Filed Apr. 24,1964, Ser. No. 362,397 14 Claims. (Cl.29-195) Thisinvention pertains to the field of hydrogen embrittle'ment of a metal.

Itllis well-known that certainmet-als such as common -4340 1 steel aresusceptible to soacalled hydrogen embrittlement. A completeunderstanding of this hydrogen embrittlement problem is unnecessary toan understanding of the present invention. Briefly, however, this prob-,lem ooncerns the fact that when a small quantity of nascent hydrogen isavailable at the surface of a metal susceptible to hydrogenembrittlement this hydrogen will tend to enterthe structure of themetal, causing a decrease to the load sustaining, capacity of the metalitself.

Itiis considered: that the most effecive means for con- "brittlement mayoccur in the presence of such metal coat- Protective metal coatings ofthis type may be applied to a metal surface in several manners. Thus,for example, a cadmium coating can be applied to a surface by a knownvacuum deposition type of process. In general the coatingsproduced inthis manner tend to be somewhat porous also with them adhesion can be aproblem. Protective coatingsi-of cadmium can also be applied byelectroplatbrittlement.

ing processes as are disclosed in the Simon et al. Patent No. 2,892,761and the Hamilton et a1. Patent No. 3,014,-

. 852 assigned to the Lockheed Aircraft Corp. The entire OOIItEIItSiOfthese patents are incorporated herein by reference forthe purpose ofamplifying upon and supplementing the contents of this specification.

An object of the present invention is to provide new and. improvedprocedures for preventing and/or controlling hydrogen embrittlement: Arelated object of this invention is to provide new and improved surfacestructures for use in combatting the problem of hydrogen em- Otherobjects of the present invention are toprovideiimethods and structures.as indicated which are comparatively inexpensive, effective and easy tocarry out and create, respectively.

These and further objects of this invention as Well as manyadvantages ofit will be more fully apparent from a detailed consideration of theremainder of this specification, the appended claims and theaccompanying drawing in which:

FIGURE 1 is an enlarged cross-sectional diagrammatic .view indicating asurface structure in accordance with this invention;

FIGURE 2 is a view similar to FIGURE 1 of a modified surface structureofthis invention; and

FIGURE 3 is a view similar to FIGURE 1 of a further modified surfacestructure of this invention.

It will [be apparent from a consideration of the drawing, and :theremainder of this specification that none of the, figures of the;drawing are intended to represent any precise structure, but that thesefigures are primarily intended for explanatory purposes. From aconsideration of the drawing and the remainder of this specification itwill be obvious to those skilled in the hydrogen em'brittlement fieldthat the present invention can be utilized in a number of dilierentmanners falling within the scope of the appended claims.

As an aid to understanding this invention it can be stated inessentially summary form that it concerns control of hydrogenembrittlement upon a metal member which is susceptible to suchcmbrittlement through the location upon such a member of one or moreoxidizing agents which: (1) are inert with respect to materials incontact with such an agent or agents; (2) are stable under the ambientconditions to Which the metal member may be subjected; and (3) arecapable of reacting with any nascent hydrogen liberated at the surfaceof the member in order to protect the metal member from hydrogenem-brittlement by combining with such hydrogen. Preferably the metalmember is coated with a protective metal coating serving to protectagainst corrosion. The oxidizing agent or agents used can be locatedupon such a protective coating. If desired a surface structure of thistype can be referred to as an article of manufacture.

This invention is best more fully explained by referring directly toFIGURE 1 of the drawing. Here there is shown a metal member such as a4340 high-strength steel member 10 having a surface 12 which is coveredwith a cadmium protective coating 14. This coating 14 may be applied tothe surface 12 by vacuum deposition techniques or as described in eitherof the aforenoted patents. In accordance with this invention the exposedsurface 16 of the coating 14 is covered with a coating or layer 18containing one or more oxidizing agents.

The purpose of this layer 18 and its function can be related to what mayoccur at the surface 12 in the absence of the layer 18. The metalcadmium is of anodic nature with respect to steel. In the presence ofhumid or especially a humid salt containing atmosphere there is atendency for a reaction to take place between those two metals. As aconsequence of this reaction it is considered that hydrogen is to adegree liberated, and that this hydrogen as a result of the lowerhydrogen over-voltage on steel as compared to cadmium will tend to enterthe steel, causing hydrogen embrittlement. It is not considerednecessary to set forth herein the exact mechanism by which such hydrogenenters the structure of the steel and acts so as to lower its strength.

The layer 18 is located directly against the coating 14 so as to be asclosely adjacent to the surface 12 as reasonably possible. Because ofthe somewhat porous, hydrogen permeable character of the layer 18 anyhydrogen liberated as a result of reactions as are indicated inpreceding paragraphs will react with an oxidizing agent disposed withinthis layer 18 to a suificient degree to provide significant protectionagainst hydrogen embrittlemcnt. Such reaction will have the effect ofimmobilizing the hydrogen, preventing it entering through the surface 12so as to cause embrittlement.

The particular layer 18 illustrated in FIGURE 1 of the drawing consistsof a mixture of at least one oxidizing agent disposed within a smallamount of an inert fluid or viscous type of composition serving as amovable binder to hold the oxidizing agent in place. Virtually any inertor substantially inert carrier type of vehicle can be employed for thepurpose of holding one or more oxidizing agents in place so as to formthe layer 18. Thus, it is possible to utilize various conventionalmineral and silicone greases and oils, fluid plasticizers such as arecommonly employed in the plastic field, petroleum jelly fractions or thelike. If desired one or more volatile solvents can be initially presentwith such vehicles for the purpose of facilitating the application of acomposition as herein described.

The oxidizing agent or agents used with this invention should be inertboth with respect to the member and to the coating 14. Also, any suchoxidizing agent or agents should be stable at the ambient conditions towhich the member 10 will be subjected during its use. Obviously any suchoxidizing agent or agents should be capable of reaction with nascenthydrogen so as to immobilize it in order to prevent such hydrogen fromentering the metal surface.

A large numer of different oxidizing agents meet these criteria.Presently preferred inorganic oxidizing agents belong to the class ofknown perborate and nitrate oxidizing agents such as sodium perborate,sodium nitrate and related alkali metal and alkaline earth compounds,although other inorganic oxidizing agents such as various permanganates,manganese dioxide, lead dioxide and the like can be used depending uponthe temperature and the degree of stress imposed on the high strengthsteel.

A number of different organic oxidizing agents can also be employed atvarious temperatures, among such peroxides are those listed in Table 4on page 78 of the text Vinyl and Related Polymers by Schildknechtpublished by John Wiley & Sons, Inc., New York, New York, 1952. Thislist is incorporated herein by reference in the interest of brevity.This list specifies various temperature operating ranges at which theperoxides listed can be used. Other organic oxidizing agents capable ofbeing used with this invention at different temperature ranges arevarious compounds capable of being used for photographic development andrelated purposes. Thus, for example, quinone, anthraquinone, benzyl,naphthaquinone, phenanthraquinone, quinonimine, various vat dyes and thelike can be employed at temperatures at which these compounds are stablein order to achieve advantages of this invention.

It is presently preferred to create a layer 18 by the simple expedientof mixing the ingredients present in this layer together and then towipe or smear this mixture on a surface. Following these operations itis normally preferred to reduce the thickness of the layer 18 to roughlythe thickness of a wiped Vaseline film by Wiping with a cloth or thelike. In general the relative proportions of the ingredients within thelayer 18 are not critical so long as this layer 18 contains as muchoxidizing material as conveniently possible. In general the higher theproportion of the oxidizing agent or agents present the more effectivethe results achieved. What is important is the presence and availabilityof an oxidizing agent to the surface 12.

As an example of how to create a layer such as the layer 18 acceptableresults can be achieved by covering cadmium coated 4340 steel surfaceswith a layer of any of the following mixtures, and then wiping theselayers with a cloth so as to leave only a thin film:

Composition 1.-50 parts by weight benzoyl peroxide; 50 parts by weighttricresyl phosphate; 10 parts by weight toluene.

Composition 2.-50 parts by weight benzoyl peroxide; 50 parts by weightof a conventionally known inert silicone oil such as the silicone oilproduced by the Dow Chemical Corporation of Midland, Michigan, and soldunder the trade name designation DC200.

Composition 3.-20 parts by weight sodium nitrate and 80 parts by weightof the inert silicone oil specified in the preceding composition 2 (inthis case the ingredients should be milled together so as to obtain anintimate mixture).

In FIGURE 2 of the drawing there is shown a metal member 20corresponding to the member 10 having a surface 22 holding a relativelyporous cadmium coating 24. This coating 24 can be applied to thissurface 22 by known vacuum deposition techniques so as to be of a porouscharacter. In the drawing this coating 24 has been hatched so as tosimulate to as great a degree as possible its porous character. Thepores within this coating 24 are filled with at least one oxidizingagent 26 as described in the preceding.

The pores may be filled with an organic oxidizing agent as described inthe preceding by merely forming a solvent solution of such an agent suchas a saturated solution of benzoyl peroxide in benzene and thenimpregnating the coating 24 in the known manner in which capacitors arevacuum impregnated with a dielectric material. After this is done thesolvent is of course removed by vaporization. Such impregnation may berepeated several times in order to assure the presence of as muchoxidizing agent in the pores as reasonably possible. In the same manneran aqueous solution of sodium nitrate may be applied to a porous cadmiumsurface 24 and the water removed as soon as possible by vaporization,leaving sodium nitrate within the pores of the coating 24.

In FIGURE 3 of the drawing there is shown another metal member 3t)corresponding to the member 10 previously described which has a surface32 covered by an adherent coating 34 of a cadmium-nickel alloy typecomposition serving to provide protection against corrosion. Thenormally exposed surface 36 of the coating 34 is covered with anadherent layer 38 of a paint or lacquerlike character containing one ormore oxidizing agents capable of being used with this invention, andconventional inert ingredients serving as a permanent binder. Theparticular construction shown in FIGURE 3 is considered to beparticularly desirable for use where the member 39 is subjected torelatively high temperatures.

The layer 38 may consist of one or more oxidizing agents as indicated inthe preceding discussion dispersed within virtually any type of a paintor lacquer-like binder composition. Such compositions are, of course,much more stable and resistant to removal than compositions such as arecapable of being used in creating the layer 18 previously described. Ifan inorganic oxidizing agent or if inorganic oxidizing agents are to beemployed in the coating 38 such material or materials can be handled insubstantially the same manner as any fillers or pigments within paint orlacquers, and such paints or lacquers can be either of a type which cureby virtue of the presence of one or more catalysts within them promotingthe reaction of a polymerized or partially polymerized ingredients or ofa solvent-release non-curing type. The organic oxidizing agents used informing a layer such as the layer 38 preferably are only employed withso-called non-curing type paint or lacquer compositions in order toavoid any possibility of these compounds entering into reactions withthese compositions. The amount of one or more oxidizing agents used inany of these types of compositions should preferably correspond to theamount of filler and pigment conventionally used in a paint or lacquer.

As an example as to how a coating such as the coating 38 may be created,it may be merely created from a lacquer type of composition containing:15 parts by weight of a Well known vinyl chloride-vinyl acetate-vinylalcohol co-polymer such as is sold under the trade name designationVAGI-I by the Carbide and Carbon Corporation, New York, New York; 3parts by weight tricresyl phosphate; 5 parts by weight benzoyl peroxide;30 parts by weight methyl isobutyl ketone; and 30 parts by weighttoluene. This composition can be applied and dried in the same manner asany conventional lacquer. If desired one half of the benzoyl peroxide inthis composition can be replaced by lauroyl peroxide.

An inorganic type paint type of composition capable of being used increating a layer such as the layer 38 can be manufactured from: 20 gramssodium nitrate; 22.8 grams raw linseed oil; 3.6 grams turpentine; and0.6 gram Japan drier in the same manner in which a paint ismanufactured. This composition can be used in substantially the samemanner as any conventional paint.

If desired, this composition can be modified so as to substitute for apart of the sodium nitrate, such as one half of the sodium1nitrate,yanequivalent weight of sodium perborate..

From a careful consideration of this specification those skilled in: thefield of hydrogen embrittlement will realize that themeans hereindescribed for controlling such embrittlementare comparativelyinexpensive, simple to use or apply and, effective. Such individualswill further realize that an important aspect of the present inventionlies not in precise proportions ofan oxidizing agent used, but in thepresence of such an oxidizing agent adjacent to: a surface; susceptibleto hydrogen embrittlement when this agent is needed in order to reactwith hydrogen. Because; of the: nature of this invention it is to beconsidered as being limited solely, bythe appended claims forming a partof this disclosure.

Weclaim:

, 1. An article of manufacture which comprises:

a high-strength steel member of a type susceptible to hydrogenembrittlement, said member having a surface; i

a porous, hydrogen-permeable metal coating covering said surfaceyandanoxidant located adjacent to said coating, said oxidant beingchemically inert with respect to said steel member, being stable underthe ambient conditions to which said steel member may be subjected andbeing capable ,of reaction with nascent hydrogen at the surface. of saidsteel member in order toprevent hydrogen from entering said surface.

2..1Anarticle of manufacture which comprises:

a metal member susceptible of hydrogen embrittlement,

said memberhaving a surface; 1.

a porous, hydrogen-permeable metal coating located against said surface;and

an oxidizing agent selected from the group comprising alkali metalperborates, alkaline earth perborates, alkali metal nitrates, alkalineearth nitrates, permanganates, manganese dioxide, lead dioxide, benzoylperoxide, quinone, anthraquinone, benzil, naphthaquinone,phenanthraquinone, and quinonimine, located adjacent to saidsurface,said oxidizing agent being capable of reacting with any hydrogenliberated as a result of anodic reaction between said metal member, andsaid metal coating in order to protect said. metal member from hydrogenembrittlement resulting from such liberation of hydrogen.

3.:An article of manufacture as defined in claim 2 wherein said metalcoating is selected from the group comprising cadmium, andnickel-cadmium alloy.

4.An article of manufacture as defined in claim 2 including an organicviscous liquid binder carrying said oxidizing agent.

5.3;An, article of manufacture as defined in claim 3 wherein said binderis selected from the group comprising mineral oil, mineral grease, fluidplasticizers, petroleum jelly fractions, silicone oil, and siliconegrease.

6. In the combination of a metal member susceptible to hydrogenembrittlement having a surface covered with a porous protective metalcoating serving to protect said surface against corrosion, theimprovement which comprises:

an tadherent layer located adjacent to said surface in contact with saidprotective metal coating, said adherent layer comprising the combinationof:

a co-polymer vehicle comprising;

vinyl chloride-vinyl acetate-vinyl alcohol; an adherent comprising;

a mixture of tricresyl phosphate and benzoyl peroxide; and a solventcomprising;

a mixture of methyl isobutyl ketone and toluene; said layer beingreactive with nascent hydrogen at the surface of said metal member inorder to protect said metal member from hydrogen embrittlement.

7. A method of controlling hydrogen embrittlement at the surface of ametal member which is susceptible to such embrittlement which comprisesthe step of locating adjacent to the surface of said metal member anoxidizing agent which is substantially chemically inert with respect tosaid metal member, which is stable under ambient conditions and which iscapable of reacting with any nascent hydrogen at the surface of saidmetal member and thereby protect said metal member from hydrogenembrittlement by combining with such hydrogen.

8. A method as defined in claim 7 wherein said metal member is a steelmember.

9. A method as defined in claim 8 wherein said metal member is coatedwith an adherent metal coating containing cadmium, said metal coatingserving to protect said metal member against corrosion.

10. A method as defined in claim 9 wherein said metal coating is porousand wherein said oxidizing agent is located within the pores of saidmetal coating.

11. A method as defined in claim 8 wherein said oxidizing agent islocated upon the surface of said metal coating and is secured to thesurface of said metal member by a viscous liquid binder.

12. In the combination defined in claim 6 wherein said adherentincludes:

lauroyl peroxide.

13. In the combination of a metal member susceptible to hydrogenembrittlement having a surface covered with a porous protective metalcoating serving to protect said surface against corrosion, theimprovement which comprises:

an adherent layer located adjacent said surface in contact with saidprotective metal coating, said layer comprising:

a vehicle mixture of linseed oil, turpentine, and

Japan dryer; and, an adherent comprising:

sodium nitrate, said layer being reactive with nascent hydrogen at thesurface of said metal member and thereby protect said member againsthydrogen embrittlement.

14. In the combination defined in claim 13 wherein said adherentincludes:

sodium perborate.

References Cited by the Examiner UNITED STATES PATENTS 1,673,271 6/1928Stewart 14814 2,892,761 6/1959 Simon et al. 204-50 3,178,321 4/1965Satterfield 14814 3,181,978 5/1965 Weiner 14814 HYLAND BIZOT, PrimaryExaminer.

DAVID L. RECK, Examiner.

R. O. DEAN, Assistant Examiner.

1. AN ARTICLE OF MANUFACTURE WHICH COMPRISES: A HIGH-STRENGTH STEELMEMBER OF A TYPE SUSCEPTIBLE TO HYDROGEN EMBRITTLEMENT, SAID MEMBERHAVING A SURFACE; A POROUS, HYDROGEN-PERMEABLE METAL COATING COVERINGSAID SURFACE; AND AN OXIDANT LOCATED ADJACENT TO SAID COATING, SAIDOXIDANT BEING CHEMICALLY INERT WITH RESPECT TO SAID STEEL MEMBER, BEINGSTABLE UNDER THE AMBIENT CONDITIONS TO WHICH SAID STEEL MEMBER MAY BESUBJECTED AND BEING CAPABLE OF REACTION WITH NASCENT HYDROGEN AT THESURFACE OF SAID STEEL MEMBER IN ORDER TO PREVENT HYDROGEN FROM ENTERINGSAID SURFACE.